When to open up the nest boxes?

[the lemon tree]

My chickens are about 15 weeks old- I've boarded up access to their nest box. When should I open this up and throw some fake eggs in there?

 

[Cats Critters]

I'd open them about 18-19 weeks.

 

[ColoradoMike]

Our RSL laid a soft shell/broken egg last week (at 16 1/2 weeks) so I decided to open up the nest boxes for business right then and there. On Monday we got our first normal egg and she's laid one a day since (she must lay mid morning, because there's never an egg when I let them out of the coop in the early AM). All three eggs have been in the nest boxes - she used the same box for the first two and tried the other box out yesterday for the third. I'm eager to get home for work today to see if she laid again and where...

So, our RSL started on the early side (~17 weeks). Our BR and Cali White haven't started squatting yet, but the BR sure looks ready in her body, but her comb and wattles have a little ways to go I think...

 

[ging3rhoffman]

We opened out nest up at 16 weeks of age and the following week we had our first egg. When we opened them up that first week it was so cute to watch them take turns looking inside and going inside. They were so curious about those wooden eggs in there.